In particle physics hexaquarks, alternatively known as sexaquarks,^[1] are a large family of hypothetical particles, each particle consisting of six quarks or antiquarks of any flavours. Six constituent quarks in any of several combinations could yield a colour charge of zero; for example a hexaquark might contain either six quarks, resembling two baryons bound together (a dibaryon), or three quarks and three antiquarks.^[2] Once formed, dibaryons are predicted to be fairly stable by the standards of particle physics.

A number of experiments have been suggested to detect dibaryon decays and interactions. In the 1990s, several candidate dibaryon decays were observed but they were not confirmed.^[3][4][5]

There is a theory that strange particles such as hyperons^[6] and dibaryons^[7] could form in the interior of a neutron star, changing its mass–radius ratio in ways that might be detectable. Accordingly, measurements of neutron stars could set constraints on possible dibaryon properties.^[8] A large fraction of the neutrons in a neutron star could turn into hyperons and merge into dibaryons during the early part of its collapse into a black hole^{[citation needed]}. These dibaryons would very quickly dissolve into quark–gluon plasma during the collapse, or go into some currently unknown state of matter.

D-star hexaquark

In 2014, a potential dibaryon was detected at the Jülich Research Center at about 2380 MeV. The center claimed that the measurements confirm results from 2011, via a more replicable method.^[9][10] The particle existed for 10⁻²³ seconds and was named d*(2380).^[11] This particle is hypothesized to consist of three up and three down quarks, and has been proposed as a candidate for dark matter.^[12][13][14]

It is theorized that groups of d-star particles could form Bose–Einstein condensates due to prevailing low temperatures in the early universe, a state in which they overlap and blend together, a bit like the protons and neutrons inside atoms. Under the right conditions, BECs made of hexaquarks with trapped electrons could behave like dark matter.^[15] According to the researchers, this result indicates that during the earliest moments after the Big Bang, as the cosmos slowly cooled, stable d*(2830) hexaquarks could have formed alongside baryonic matter, and the production rate of this particle would have been sufficient to account for the 85% of the Universe's mass that is believed to be dark matter.^[16]

Critics say that even if it is possible to create a d* condensate as proposed, it cannot survive the intense radiation of the early Universe. Once they are blasted apart, there is no way to create more d* particles capable of forming a Bose-Einstein condensate, as the conditions that admit their creation will have passed.^[17]

H dibaryon

In 1977, Robert Jaffe proposed that a possibly stable H dibaryon with the quark composition udsuds could notionally result from the combination of two uds hyperons.^[18] Calculations have shown that this particle is light and (meta)stable. It actually takes more than twice the age of the universe to decay. Data constrains the existence of such a particle, and it turns out that it is still allowed.^{[1][19][20][21][22][23]} As per one analysis, a hypothetical SU(3) flavor-singlet, highly symmetric, deeply bound neutral scalar hexaquark S=uuddss, which due to its features has escaped from experimental detection so far, may be considered as a candidate for a baryonic dark matter. However, existence of this state may contradict the stability of oxygen nuclei, necessitating further thorough analysis of it.^[24]

Others

• In 2022 Riken researchers studied the existence of triply charmed dibaryon ${\displaystyle \Omega _{ccc}\Omega _{ccc))$ concluding computationally that it should fall within a feasible regime.^[25][26]